®
RT8298A
6A, 24V, 600kHz Step-Down Converter with Synchronous
Gate Driver
General Description
The RT8298A is a synchronous step-down DC/DC converter
with an integrated high side internal power MOSFET and
a gate driver for a low side external power MOSFET. It
can deliver up to 6A output current from a 4.5V to 24V
input supply. The RT8298A's current mode architecture
allows the transient response to be optimized over a wider
input voltage and load range. Cycle-by-cycle current limit
provides protection against shorted outputs and soft-start
eliminates input current surge during start-up. The
RT8298A is synchronizable to an external clock with
frequency ranging from 300kHz to 1.5MHz.
The RT8298A is available in SOP-8 (Exposed Pad)
packages.
Features
4.5V to 24V Input Voltage Range
6A Output Current
45mΩ Internal High Side N-MOSFET
Ω
Current Mode Control
600kHz Switching Frequency
Adjustable Output from 0.8V to 15V
Up to 95% Efficiency
Internal Compensation
Stable with Ceramic Capacitors
Synchronous External Clock : 300kHz to 1.5MHz
Cycle-by-Cycle Current Limit
Input Under Voltage Lockout
Output Under Voltage Protection
Power Good Indicator
Thermal Shutdown Protection
Force PWM Turn On
RoHS Compliant and Halogen Free
Ordering Information
RT8298A
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
½
Applications
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
Point of Load Regulator in Distributed Power System
Digital Set top Boxes
Personal Digital Recorders
Broadband Communications
Flat Panel TVs and Monitors
½
Simplified Application Circuit
V
IN
C
IN
SW
VCC
C
VCC
FB
Chip Enable
EN/SYNC
GND
R2
BG
Q1
R1
C
OUT
VIN
RT8298A
BOOT
C
BOOT
L
V
OUT
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8298A-00 July 2014
www.richtek.com
1
RT8298A
Marking Information
RT8298AGSP : Product Number
Pin Configurations
(TOP VIEW)
SW
BOOT
VCC
BG
2
3
4
8
RT8298A
GSPYMDNN
YMDNN : Date Code
VIN
EN/SYNC
FB
GND
GND
9
7
6
5
SOP-8 (Exposed Pad)
Functional Pin Description
Pin No.
1
2
3
4
Pin Name
SW
BOOT
VCC
BG
Pin Function
Switching Node. Output of the internal high side MOSFET. Connect this pin to
external low-side N-MOSFET, inductor and bootstrap capacitor.
Bootstrap for High side Gate Driver. Connect a 1F ceramic capacitor between the
BOOT pin and SW pin.
BG Driver Bias Supply. Decouple with a 1F X5R/X7R ceramic capacitor between
the VCC pin and GND.
Gate Driver Output. Connect this pin to the gate of the external low-side
N-MOSFET.
Ground. The exposed pad must be soldered to a large PCB and connected to GND
for maximum thermal dissipation.
Feedback Input. This pin is connected to the converter output. It is used to set the
output of the converter to regulate to the desired value via an external resistive
divider. The feedback reference voltage is 0.808V typically.
Enable or External Frequency Synchronization Input. A logic-high (2V < EN <
5.5V) enables the converter; a logic-low forces the IC into shutdown mode
reducing the supply current to less than 3A. For external frequency
synchronization operation, the available frequency range is from 300kHz to
1.5MHz.
Power Input. The available input voltage range is from 4.5V to 24V. A 22F or
larger input capacitor is needed to reduce voltage spikes at the input.
5,
GND
9 (Exposed Pad)
6
FB
7
EN/SYNC
8
VIN
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS8298A-00 July 2014
RT8298A
Function Block Diagram
VIN
VCC
V
CC
Internal
Regulator
OSC
Slope
Current Sense
Compensator Amplifier
+
-
EN/SYNC
5k
Enable
Comparator
+
1.7V
-
3V
R
SENSE
Foldback
Control
OTP
V
CC
BOOT
UV Comparator
V
CC
6nA
0.808V
V
SS
15pF
FB
54pF
+
+
EA
-
0.4V
+
-
Switch
Controller
Current
Signal
COMP
+
-
45m
SW
Current
Comparator
BG
Driver
BG
300k
1pF
Operation
The RT8298A is a synchronous high voltage Buck
Converter that can support the input voltage range from
4.5V to 24V and the output current can be up to 6A. The
RT8298A uses a constant frequency, current mode
architecture. In normal operation, the high side N-MOSFET
is turned on when the Switch Controller is set by the
oscillator (OSC) and is turned off when the current
comparator resets the Switch Controller. While the N-
MOSFET is turned off, the external low side N-MOSFET
is turned on by BG Driver with 5V driving voltage from
Internal Regulator (V
CC
) until next cycle begins.
High side MOSFET peak current is measured by internal
R
SENSE
. The Current Signal is where Slope Compensator
works together with sensing voltage of R
SENSE
. The error
amplifier EA adjusts COMP voltage by comparing the
feedback signal (V
FB
) from the output voltage with the
internal 0.808V reference. When the load current
increases, it causes a drop in the feedback voltage relative
to the reference, the COMP voltage then rises to allow
higher inductor current to match the load current.
UV Comparator : If the feedback voltage (V
FB
) is lower
than threshold voltage 0.4V, the UV Comparator's output
will go high and the Switch Controller will turn off the high
side MOSFET. The output under voltage protection is
designed to operate in Hiccup mode.
Oscillator (OSC) : The internal oscillator runs at nominal
frequency 600kHz and can be synchronized by an external
clock in the range between 300kHz and 1.5MHz from EN/
SYNC pin.
Enable Comparator : Internal 5kΩ resistor and Zener diode
are used to clamp the input signal to 3V. A 1.7V reference
voltage is for EN logic-high threshold voltage. The EN pin
can be connected to VIN through a 100kΩ resistor for
automatic startup.
Foldback Control : When V
FB
is lower than 0.7V, the
oscillation frequency will be proportional to the feedback
voltage.
Soft-Start (SS) : An internal current source (6nA) charges
an internal capacitor (15pF) to build the soft-start ramp
voltage (V
SS
). The V
FB
voltage will track the internal ramp
voltage during soft-start interval. The typical soft-start time
is 2ms.
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8298A-00 July 2014
www.richtek.com
3
RT8298A
Absolute Maximum Ratings
(Note 1)
–0.3V
to 26V
–0.3V
to (V
IN
+ 0.3V)
–5V
to 30V
–0.3V
to 6V
−0.3V
to 6V
1.333W
Supply Input Voltage, V
IN
------------------------------------------------------------------------------------------
Switching Voltage, SW --------------------------------------------------------------------------------------------
SW (AC) < 20ns -----------------------------------------------------------------------------------------------------
BOOT to SW ---------------------------------------------------------------------------------------------------------
All Other Voltage ----------------------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
SOP-8 (Exposed Pad) ---------------------------------------------------------------------------------------------
Package Thermal Resistance (Note 2)
SOP-8 (Exposed Pad),
θ
JA
---------------------------------------------------------------------------------------- 75°C/W
SOP-8 (Exposed Pad),
θ
JC
--------------------------------------------------------------------------------------- 15°C/W
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------- 260°C
Junction Temperature ----------------------------------------------------------------------------------------------- 150°C
Storage Temperature Range --------------------------------------------------------------------------------------
–65°C
to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------- 2kV
MM (Machine Model) ----------------------------------------------------------------------------------------------- 200V
(Note 4)
Recommended Operating Conditions
Supply Input Voltage, V
IN
------------------------------------------------------------------------------------------ 4.5V to 24V
Junction Temperature Range --------------------------------------------------------------------------------------
−
40°C to 125°C
Ambient Temperature Range --------------------------------------------------------------------------------------
−
40°C to 85°C
Electrical Characteristics
(V
IN
= 12V, T
A
= 25°C, unless otherwise specified)
Parameter
Shutdown Supply Current
Supply Current
Feedback Reference Voltage
Feedback Current
High-Side Switch On Resistance
High-Side Switch Current Limit
Oscillation Frequency
Short Circuit Oscillation Frequency
Maximum Duty Cycle
Minimum On-Time
Input Under Voltage Lockout Threshold
Input Under Voltage Lockout Threshold
Hysteresis
Symbol
Test Conditions
V
EN
= 0V
V
EN
= 3V, V
FB
= 1V
Min
--
--
--
--
--
--
--
--
--
4
--
Typ
1
0.9
10
45
10
600
190
90
100
4.2
400
Max
--
--
0.82
--
--
--
--
--
--
--
4.4
--
Unit
A
mA
V
nA
m
A
kHz
kHz
%
ns
V
mV
V
REF
I
FB
R
DS(ON)
4.5V
V
IN
24V
V
FB
= 0.8V
BOOT
SW = 4.8V
0.796 0.808
f
OSC1
f
OSC2
D
MAX
t
ON
V
UVLO
V
UVLO
V
FB
= 0V
V
FB
= 0.6V
V
FB
= 1V
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS8298A-00 July 2014
RT8298A
Parameter
EN Threshold
Voltage
Logic-High
Logic-Low
Symbol
V
IH
V
IL
f
Sync
t
OFF
V
EN
= 2V
T
SD
T
SD
V
CC
R
Sink
R
Source
Test Conditions
Min
2
--
0.3
--
--
--
--
4.5
--
--
Typ
--
--
--
10
1
150
20
5
0.9
3.3
Max
5.5
0.4
1.5
--
--
--
--
--
--
--
Unit
V
MHz
s
A
C
C
V
Sync Frequency Range
EN Turn-Off Delay
EN Pull Low Current
Thermal Shutdown
Thermal Shutdown Hysteresis
BG Driver Bias Supply Voltage
Gate Driver Sink Impedance
Gate Driver Source Impedance
Note 1.
Stresses beyond those listed
“Absolute
Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect
device reliability.
Note 2.
θ
JA
is measured at T
A
= 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7.
θ
JC
is
measured at the exposed pad of the package.
Note 3.
Devices are ESD sensitive. Handling precaution is recommended.
Note 4.
The device is not guaranteed to function outside its operating conditions.
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8298A-00 July 2014
www.richtek.com
5
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